Conventional micro-electromechanical system based (MEMS-based) oscillators employ various techniques to avoid latch-up effects. Latch-up effects occur when an oscillator generates two differential outputs of which one stays at a high voltage (e.g., an internal supply voltage VDD) and the other one stays at a low voltage (e.g., an internal ground voltage VSS). Thus, an oscillator experiencing latch-up typically does not generate any oscillation signal. One approach involves adding a capacitor to the source ends of the oscillation ring to increase the effective transconductance of the oscillation ring. In general, the larger the capacitance of the added capacitor, the greater the effective transconductance, and thus, the more likely the latch-up effect can be avoided.
However, in order to prevent various relaxation oscillation conditions, the capacitance of the added capacitor typically does not exceed the load capacitance of the oscillation ring. Depending on the size of the load capacitance, the added capacitor might be restrained from providing sufficient capacitance for boosting the effective transconductance. As such, the added capacitor might be insufficient to avoid latch-up effects while preventing relaxation oscillation conditions at the same time. An alternative approach involves increasing the operational current of the oscillation ring, which helps increase the effective transconductance of the oscillation ring. This alternative approach, however, demands a greater power consumption, which might introduce various design constrains for a circuit that incorporates the oscillator.
In addition to latch-up effects, conventional MEMS-based oscillators typically exhibit parasitic effects due to the parasitic inductance of the bonding wires. These bonding wires can be found between a MEMS chip and an integrated circuit interacting with the MEMS chip. Under certain conditions, these parasitic effects may disrupt the operations of an oscillator. For instance, the parasitic effects of the bonding wires can push the loop gain of the oscillator above unity at a parasitic parallel resonant frequency (PPRF). As a result, an oscillator having these parasitic effects may generate a noise signal that oscillates outside of its intended operational frequency range.
In view of the aforementioned issues, there is a need for a low power low noise oscillator to minimize latch-up effects and parasitic effects experienced by the conventional oscillators.